1. Field of the Invention
The present invention relates to a CDMA receiver terminal for use in a CDMA communications system, and more particularly, to a CDMA receiver terminal for receiving a signal transmitted by a base station using two antennas in a transmission diversity mode.
2. Description of the Related Art
Conventionally, some CDMA communications systems have employed a method of transmitting signals from a base station to a receiver terminal as illustrated in FIG. 1, wherein base station 1 uses two antennas ANT1, ANT2 to transmit signals A, B to a receiver terminal 2 (hereinafter called the “transmission diversity mode”).
Receiver terminal 2 inversely spreads the signals transmitted from respective antennas ANT1, ANT2 of base station 1 in finger unit (inverse spreader unit), corrects the signals for the phase in finger unit (phase corrector unit), and then combines the resulting signals in RAKE circuit. Finger unit (inverse spreader unit) and finger unit (phase corrector unit) each comprises a plurality of finger circuits, each of which performs the foregoing operation at a predetermined operating clock. Each of the finger circuits in finger unit (inversely spreader circuit) corrects the timing of the operating clock based on a timing control pulse signal applied from a timing corrector circuit (not shown) provided externally to receiver terminal 2.
Now, the configuration of each finger circuit in finger unit (phase corrector unit) provided in the conventional CDMA receiver terminal will be described with reference to FIG. 2.
Referring to FIG. 2, the finger circuit of the prior art example comprises phase estimator circuit 17, phase corrector circuits 18, 19, and antenna combiner circuit 20. Each of the components operates based on an operating clock supplied from TCXO (Temperature Compensated Crystal Oscillator) 16.
Phase estimator circuit 17 estimates the amounts of phase correction for signals received from antenna ANT1, ANT2 from base station 1 (see FIG. 1) based on a difference in phase between I, Q phase points of known expected data and inverse spread data inversely spread in finger unit (inverse spreader unit) at the previous stage. Phase estimator circuit 17 also applies the inverse spread data inversely spread in finger unit (inverse spreader unit) to phase corrector circuits 18, 19.
Phase corrector circuit 18 corrects the phase of the inverse spread data for the received signal from antenna ANT1 of base station 1, out of the inverse spread data applied from phase estimator circuit 17, by the amount of phase correction estimated by phase estimator circuit 17. Phase corrector circuit 19 corrects the phase of the inverse spread data for the received signal from antenna ANT2 of base station 1, out of the inverse spread data applied from estimator circuit 17, by the amount of phase correction estimated in phase estimator circuit 17. Each of phase corrector circuits 18, 19 applies the phase-corrected inverse spread data to antenna combiner circuit 20.
Antenna combiner circuit 20 combines the phase-corrected inverse spread data applied from respective phase corrector circuits 18, 19.
In the conventional CDMA receiver terminal as described above, however, since the finger unit (phase corrector unit) and timing corrector circuit are operating irrespective of the validity of received signals transmitted from respective antennas ANT1, ANT2 of base station 1, there is a problem that this constitutes a factor of increasing the power consumption.